CDI troubleshooting question for 1990 90hp V4 crossflow rectifier/regulator

[havoc_squad]

I have a 1990 90hp V4 crossflow that I recently finished rebuilding and have been ironing out the minor bugs identified.
(1 hour or less of run time, under break in procedure being gentle checking things out on the hose)
I noticed that the tachometer failed to register after I finished checking all the essentials first on the first 15 min run which held a steady clean idle at 1000 rpm.

I know for a fact it worked correctly before the engine rebuild.

Everything was hooked up per the OEM service manual instructions before any power was applied to anything.

All clean battery and wiring harness terminals firmly secured to posts. Standard wet cell marine battery. Battery terminals were never reversed.

I grabbed the CDI electronics troubleshooting guide and did the following while all wire connections properly attached while running:

1. At 1000 rpms, verified purple wire voltage at wire terminal to regulator/rectifier was close (I can't remember it exactly, but I believe it was around 12.5 volts with 0.25 volt difference)

2. With engine at 1500 rpm, check the difference in voltage of each of the yellow wires (yellow solid vs yellow/gray stripe) against ground. (Using DVA adapter)

17 volts on solid yellow, 32 volts on yellow/gray stripe (or it was vice versa)

So, my question is, on the directed step 4 listed on CDI troubleshooting guide safe to do on the OMC/BRP regulator/rectifier? That is, make a mark on both of the bottom yellow/gray stripe wires and on one side of the buss swap/exchange the yellow solid for the yellow/gray stripe. Then restart the motor and perform the same test at 1500rpm.

The terminal with the mark that has the lowest voltage in comparison is the component that is at fault, correct?

As a bonus, I did step 5 after step 2 to see what the tachometer was showing and oddly enough, it was showing 8 volts on DVA adapter. Looked up and the tach was working for a bit. Did a couple other things and it was gone. Checked it again and the voltage dropped to like 1 to 2 volts.

Don't know if the voltage being supplied to tach got shut off when the battery got close to being charged up as a consequence of whatever damage done to the regulator (I assume).

Is there anything I should think about checking after I replace the regulator/rectifier that can be a hidden threat to them?

 

[havoc_squad]

I never was able to pinpoint exactly where/when the reverse polarity incident happened.

I was however able to diagnose it as a damaged rectifier/regulator without doing that stator wire swap with the marked wires. A bench test was sufficient to diagnose it after a potential regulator/rectifier issue was identified from the previous engine running tests done.

I drew an electronic diagram of the most likely design of the system and started doing diode testing with no power and the rectifier/regulator wires disconnected.

When I got to the yellow/gray wire going to positive wire direction, there was no voltage drop on the diode mode, which told me there was at least one bad diode with an open short (open short is better than shorted diode).

In looking at the drawing I made, it appeared it should be possible to do a diode test from ground going the direction to either of yellow/yellow-gray wires regardless of whatever regulator circuit exists on it.

Both of those showed no voltage drop for diode mode, which means to me those are also bad, open diodes.

Is it possible for the stator or regulator/rectifier to hold a charge when moving the flywheel by hand with battery unplugged?

 

[Faztbullet]

Nope.... A lot of people coat the rect/reg mounting gasket and forget to install the grounding washer on the bolt. This will cause a weak ground between rect/reg and block and diode cannot bleed off and fails.

 

[havoc_squad]

Nope.... A lot of people coat the rect/reg mounting gasket and forget to install the grounding washer on the bolt. This will cause a weak ground between rect/reg and block and diode cannot bleed off and fails.

I kind of suspected that issue, that's why I bought two of those ground washers, one for each side on the parts schematic. Do I need to clean off any aviation form a gasket on the threads of the bolt threads as well before I install?

 

[Faztbullet]

yes...

 

[oldboat1]

Might try the bench test on p. 8: https://www.cdielectronics.com/wp-content/uploads/2013/02/CDI Troubleshooting Guide - 2012.pdf

 

[havoc_squad]

I stopped when the next step on the running test was to swap stator wires and did bench test instead, the diode failed on diode test mode (open diode) on the multimeter for yellow/gray striped side to positive

The yellow/gray was also the terminal that had the most voltage on DVA reading, which makes sense because the diode on that side failed as open and blocked current flow, causing high voltage compared to the solid yellow side diode DVA volyage which was still working.

I've already replaced the part and ensured the short bolts had grounding washers, the threads had been cleaned off of aviation form a gasket on those grounding bolts, and torqued them to spec on the inch pounds to rule out bad grounding.

If I get a bad ground still after this that fries the replacement, I'm probably going to take it to a professional nearby that I trust.

 

[oldboat1]

good progress, seems to me. Don't forget to make sure the gasket is good or replaced.

 

[havoc_squad]

good progress, seems to me. Don't forget to make sure the gasket is good or replaced.

The gasket was barely used. In an emergency I would not hesitate to re-use it but I already bought one to go with the new regulator/rectifier.